Subject TIB_LookupCombo to allow selecting
I am familiar with the basic steps of setting up a TIB_LookupCombobox
to look up a foreign key from a different table. Now how do I allow
that the user selects <none> in the lookup combo, so that the foreign
key is set to NULL? Once an entry is choosen via the lookup, I can
switch to different entries, but not back to NULL.

Any ideas?